1. Field of the Invention
The present invention relates generally to medical devices directed to the prevention of luminal occlusion, and more particularly to stents and methods for making and utilizing these stents in the treatment of both benign and malignant conditions wherein the functionality of the stents is determined by geometrical variability of the scaffolding and concomitant interstices.
2. Description of Related Art
Stents are devices that are inserted into a vessel or passage to keep the lumen open and prevent closure due to a stricture, external compression, or internal obstruction. In particular, stents are commonly used to keep blood vessels open in the coronary arteries and they are frequently inserted into the ureters to maintain drainage from the kidneys, the bile duct for pancreatic cancer or cholangiocarcinoma or the esophagus for strictures or cancer. Vascular as well as not vascular stenting has evolved significantly; unfortunately there remain significant limitations with respect to the technology for producing stents suitable to various portions of a patient's anatomy.
Historically, in order to provide a stent with varying characteristics, the stent had to be manufactured from multiple materials, at least one for each characteristic desired. As a result, many of these stents are woven from two or more metals having differing shape-memories for example. Unfortunately, braided stents are vulnerable to premature obsolescence. Moreover, providing multiple material types in a single stent may lead to inconsistent characteristics along the surface area of the stent. This is particularly undesirable when the stent is to be placed in vascular or nonvascular lumens that have been occluded for one reason or another. The stent needs to be stiffer in some regions while more flexible in others. Moreover, as stents become more readily accepted, additional applications will develop.
Radiation therapy is the careful use of high-energy radiation to treat cancer. Particularly, the radiation destroys the cancer cells' ability to reproduce and the body naturally gets rid of these cells. Radiation therapy is a broad term that also includes the use of potentiating agents such as chemotherapy to enhance the radiation efficacy range. Alternatively, a radiation oncologist may use radiation generated by a machine outside a patient's body (external beam radiation therapy). Radiation also may be given with radioactive sources that are put inside the patient (brachytherapy). Unfortunately, both machine and intravenous radiation therapy treatments depend to some extent on systemic delivery. As a result, collateral tissue exposure to the radiation is inevitable. Larger doses of radiation or potentiating agents are required to ensure adequate delivery of a pharmacological effective dosage reaches the target tissue. This results in side effects such as tissue damage, fatigue, fatigue, skin irritation, temporary or permanent hair loss, temporary change in skin color in the treatment area, loss of appetite, nausea and vomiting, sluggish bowels, cramps and diarrhea, infertility or sterility, vaginal dryness or narrowing, impotence and in some cases death. Radiation therapy also can increase your risk of developing a second cancer. These effects generally result from the high doses required to ensure the radiation gets to the target tissue.
Additional limitations of existing devices involve the constraint of flow dynamics through the internal diameter because of their scaffolding architecture. In particular, depending on whether a stent is covered or formed from braided filaments, flow dynamics can be adversely affected. In certain cases, covered stents can cause or exacerbate mucostassis as a result of the interaction of the polymer side chains and the mucous.
Therefore, there remains an existing need for a therapeutic stent that can have varying characteristics along its surface area while being stamped, not braded, from a single base material. Moreover, there is a need for such a therapeutic stent where the relative hardness, softness, flexibility, stiffness and radial force can be modified as a function of geometric considerations rather than material considerations. In particular, there is a need for a stent that is divided into zones so as to allow the stent to have predetermined characteristics in one zone and could conceivably have drastically different characteristics in an adjacent zone so as to allow for stents that can be tailored to anatomical lumens in general and the particular lumen topography of a specific patient in particular. Moreover, a need remains for a stent that is specifically designed to resist adhesion and facilitate the flow of fluids generally and viscid fluids in particular. There also remains a need for the design of radioactive implantable devices that emit predetermined amounts of radiation at the site of implantation to alleviate radiation side effects associated with systemic delivery of radiation therapy. Particular interest is directed principally on the significant reduction in radiation exposure to collateral tissue. Development of implantable device coatings impregnated with radiation potentiating agents to insure radiation penetration; leveraging knowledge of site specific delivery of implantable devices to develop radiation delivery devices for difficult to access organs such as the liver is needed. Therefore, there is a need for site specific limited dosage delivery of biologicals, which creates additional sites available to radiation therapy.